Computed tomography and ultrasound examination of subcapsular prostatic cyst in a fiveyear-old dog with severe benign prostatic hyperplasia.

Clinical case: A five-year-old Bullmastiff dog was initially presented for staging of an extra skeletal osteosarcoma on the right hip. The dog had a history of intermittent haematuria for months that had never been investigated. Abdominal computed tomographic examination (CT) incidentally revealed an enlarged (8x7.6x5cm) and heterogeneous prostate with contrast enhancement and periprostatic fat stranding. Several hypoattenuating areas were observed in the parenchyma and its periphery, some of them outlined by a rim enhancement on post-contrast scan. Prostatitis and prostatic abscesses associated with secondary steatitis were suspected. Bilateral mild medial iliac lymphadenopathy was present. Ultrasound examination (US) showed an enlarged (7.6cm width, 4cm height in cross section), bilobed prostate. Anechoic dilated ducts radiated from the middle of the gland and connected with an anechoic, septated and irregular-shaped area with distal enhancement between the parenchyma and the distended prostatic capsule of the right lobe. The surrounding fat was hyperechoic, suggesting secondary steatitis. No abnormality was found in the testicles. Cytology from fluid collected by prostatic lavage (PL) showed red blood cells and prostatic cells but no inflammatory cells or bacteria. Urinalysis was within standard limits. Ultrasound-guided fine needle aspiration (US-FNA) of the subcapsular cavity and prostatic parenchyma were performed and 0.2 ml of serous fluid were collected from the cavity. No signs of inflammation were observed on cytological examination. A severe benign prostatic hyperplasia (BPH) and a subcapsular cyst were diagnosed. No US-FNA of the iliac lymph nodes was performed. The dog underwent castration at the same time as surgical removal of the hip mass. Regardless of his BPH, he received cefalexin and carprofen during one week. The dog showed no urinary symptoms during the three weeks after surgery and no ultrasound control was performed. Discussion: Small intraparenchymal cysts are common findings in BPH. Obstruction of ducts by cellular hyperplasia and hypertrophy leads to accumulation of non-inflammatory prostatic secretions within the parenchyma. We report that, while most cysts associated with BPH are located within the parenchyma, they can also collect peripherally between the prostatic parenchyma and the capsule. In this case, CT showed severe enlargement and heterogeneity of the prostate. CT is reported to be more accurate than US for evaluating prostatic size. Prostatic height may have been underestimated by US. Heterogeneous tissue structure and changes in attenuation on CT after contrast agent injection seem to be very sensitive and to detect earlier prostatic changes than US1. However, these features do not specifically differentiate between different prostatic conditions and should not be over-interpreted. Prostatic surrounding reactive fat at US or CT is usually not observed in BPH. Severe enlargement of the prostate could have led to surrounding steatitis. US is the gold standard when investigating the prostate. However, cytology is essential to distinguish between cysts and abscesses2 and to confirm a prostatitis. Cytology of fluid obtained by PL shows a good correlation with histology in case of inflammation. Dilution should be avoided by centrifugation of sample before examination. Contamination by cells of the urinary tract may occur. US-FNA permits to focus on lesion detected by US and shows the strongest correlation with histological diagnosis. Aspiration of fibrotic tissue can lead to poor cellularity.3 In this case, both methods lead to a BHP diagnosis. Increased serum canine prostatic specific esterase (CPSE) concentrations have been reported in dogs affected by HBP, prostatitis or prostatic carcinoma. CPSE could be useful to detect early prostatic disorders but further evaluations are needed to differentiate between prostatic diseases. According to anamnesis and clinical findings, cytology should be performed to refine the imaging diagnosis and propose the most accurate treatment.